Neutron diffraction, specific heat and magnetic susceptibility of Ni3(PO4)2

The Ni3(PO4)2 phosphate was synthesized by the ceramic method in air atmosphere. The crystal structure consists of a three-dimensional skeleton constructed from Ni3O14 edge-sharing octahedra, which are interconnected by (PO4)3− oxoanions with tetrahedral geometry. The magnetic behavior was studied on powdered sample by using susceptibility, specific heat and neutron diffraction data. The nickel(II) orthophosphate exhibits a three-dimensional magnetic ordering at approximately 17.1 K. However, its complex crystal structure hampers any parametrization of the J-exchange parameter. The specific heat measurements of Ni3(PO4)2 exhibit a three-dimensional magnetic ordering (λ-type) peak at 17.1 K. Measurements above TN suggest the presence of a small short-range order in this phase. The total magnetic entropy was found to be 28.1 KJ/mol at 50 K. The magnetic structure of the nickel(II) phosphate exhibits ferromagnetic interactions inside the Ni3O14 trimers which are antiferromagnetically coupled between them, giving rise to a purely antiferromagnetic structure.